Mechanism and Characteristics of Humidity Sensing with Polyvinyl Alcohol-Coated Fiber Surface Plasmon Resonance Sensor

Abstract

A surface plasmon resonance (SPR) sensor based on a side-polished single mode fiber coated with polyvinyl alcohol (PVA) is demonstrated for relative humidity (RH) sensing. The SPR sensor exhibits a resonant dip in the transmission spectrum in ambient air after PVA film coating, and the resonant wavelength shifts to longer wavelengths as the thickness of the PVA film increases. When RH changes, the resonant dip of the sensor with different film-thicknesses exhibits interesting characteristics for optical spectrum evolution. For sensors with initial wavelengths between 550 nm and 750 nm, the resonant dip shifts to longer wavelengths with increasing RH. The averaged sensitivity increases firstly and then drops, and shows a maximal sensitivity of 1.01 nm/RH%. Once the initial wavelength of the SPR sensor exceeds 850 nm, an inflection point of the resonant wavelength shift can be observed with RH increasing, and the resonant dip shifts to shorter wavelengths for RH values exceeding this point, and sensitivity as high as −4.97 nm/RH% can be obtained in the experiment. The sensor is expected to have potential applications in highly sensitive and cost effective humidity sensing.

Au nanorod–coupled microfiber optical humidity sensors

“…3(b)), from which we obtain a sensitivity of about 0.51 nm/% RH. While this sensitivity is comparable with other high-sensitivity microfiber RH sensors [10,13,16,[18][19][20][28][29][30][31], the hybrid nanorodmicrofiber sensor is much more compact in size (i.e., the 2-μm cavity size of this sensor versus > 40-μm cavity sizes of other sensors) [9][10][11][12][16][17][18][19][20][21]. The miniature cavity size is also beneficial to fast response, as has been shown in other types of microfiber optical sensors [10,25,32].…”

Smart Textile‐Based Personal Thermal Comfort Systems: Current Status and Potential Solutions

“…[360-362, 373, 374] PVA easily dissolves in hot water and can be applied to fiber or textile surfaces through coating processes. [360,375] However, research employing PVA reports moderate to high RH sensing hysteresis as well as a greater swelling at high RHs meaning it provides lower sensitivity at low RHs. [360] RH sensors that rely on PVA for sensing report small sensing ranges typically above 60% RH.…”

Optical Sensing of Humidity Using Polymer Top-Covered Bragg Stacks and Polymer/Metal Thin Film Structures

“…The sensitivity of fiber optic sensors is calculated as nm per % RH because usually for detection the wavelength shift of the signal dip is monitored. The sensitivity values reported in the literature vary in a broad range from 0.023 nm/% RH to 1.01 nm/% RH [33]. In order to make a comparison with our sensor, we calculated the resolution using Equation (2) assuming wavelength accuracy of 0.1 nm.…”